1. Field of the Invention
This invention relates to a method for manufacturing a piston of internal combustion engine, particularly to a method for forming a gallery portion of the piston.
2. Prior Art
A conventional gallery segment provided in the top of an internal combustion engine piston for the purpose of cooling is disclosed, for example, in Japanese Utility Model Publication No. 52346 of 1983. This conventional gallery segment comprises a piston-cooling cavity and ring lands that are integrally formed beforehand, and is cast in a piston body when the piston is founded. The gallery segment is made of cast iron or wear-resistant metal such as Ni-resist. Usually, however, an oil gallery portion does not require high wear-resistance. The use of such a costly wear-resistant material as Ni-resist with low thermal conductivity not only has substantially lowered the cooling effect but also resulted in cost increase.
Moreover, in such a conventional device, the wall thickness becomes large enough to provide a full gallery inside capacity and a larger gallery is required to secure the same degree of cooling effect as in a device made of aluminum. This in turn increases the size and weight of the piston.